Evidence for uptake2-mediated O-methylation of noradrenaline in the human amnion FL cell-line

The uptake and metabolism of 3H-noradrenaline has been examined in the FL cell-line derived originally from human amnion. Cell cultures metabolised 3H-noradrenaline (1.0 mumol/l) to 3H-normetanephrine and, to a lesser extent, to metabolites (not distinguished) of the O-methylated deaminated fraction; primary deaminated metabolites were not detected. 3H-normetanephrine formation a) was not saturable in the noradrenaline concentration range 0.2-150 mumol/l, b) was decreased to 20%-30% of control levels by uptake2 inhibitors (O-methylisoprenaline, 20 and 100 mumol/l; cimetidine, 10 mumol/l; hydrocortisone, 200 mumol/l) and c), was almost insensitive to uptake1 inhibitors (cocaine, 30 mumol/l; desipramine, 3 mumol/l). Uptake of noradrenaline was manifested after 30 minutes as a 6-fold increase in the cell content of the amine following inhibition of catechol-O-methyl transferase, either alone or in conjunction with inhibition of monoamine oxidase. Uptake was decreased maximally to 40% of control levels by O-methylisoprenaline. IC50 values for inhibition of the O-methylisoprenaline-sensitive component of uptake were (in mumol/l): corticosterone (0.3), papaverine (1.1), O-methylisoprenaline (3.0), cimetidine (6.0), (-)noradrenaline (460), and tetraethylammonium (2230). Except for the last agent, for which a comparative value is not available, the IC50's are in good agreement with those for inhibition of uptake2 in the Caki-1 cell-line reported by other investigators. The component of uptake resistant to O-methylisoprenaline was depressed by papaverine (a 50% decrease at 50 mumol/l), but was not affected by the other uptake2 inhibitors or by cocaine (30 mumol/l).(ABSTRACT TRUNCATED AT 250 WORDS)